Under the state Constitution, all revenues in excess of the necessary cost of collection and administration accruing to the state from motor vehicle registration fees, operators' licenses, gasoline road toll, or any other special charges or taxes with respect to the operation of motor vehicles or the sale or consumption of motor vehicle fuels are appropriated and used exclusively for the construction, reconstruction, and maintenance of public highways within this state, including the supervision of traffic thereon and for the payment of the interest and principal of bonds issued for highway purposes. All such revenues, together with federal grants-in-aid and American Recovery and Reinvestment Act funds received by the state for highway purposes, are credited to the Highway Fund. While the principal and interest on state highway bonds are charged to the Highway Fund, the assets of this fund are not pledged to such bonds.